A number of different approaches have been taken with regard to the problems of providing a composite sea-going barge-tug vessel wherein the tug or propulsion portion is detachable from the barge or cargo-carrying portion and wherein the tug is capable of operation as a seagoing tug. In general, these approaches fall into two classes, viz., "articulated" barge-tug vessels and "rigid-connected" barge-tug vessels. In an articulated vessel, the barge generally includes a notched or recessed aft portion which is hingedly attached to the bow of the tug. This form of detachable connection is disadvantageous because, inter alia, the barge and tug are permitted to pitch and roll independently of one another and this prevents use of the vessel at sea during unfavorable weather conditions.
The "rigid-connected" vessels of the prior art, while overcoming this particular disadvantage, suffer a number of important disadvantages themselves. For example, the tug, when detached from the barge, should itself be of a seaworthy design and many such detachable tugs are simply not seaworthy. Another serious disadvantage of some constructions is the complexity of the interlocking shapes which are used in connecting the barge and tug together. These complex shapes are difficult and expensive to reproduce and hence the manufacturing costs of such vessels are high. Yet another important disadvantage of the prior art is the difficulty encountered in engaging and disengaging the barge and tug.
Although, as stated, a number of different approaches have been taken, three of these such approaches will be briefly considered here for purposes of comparison. U.S. Pat. No. 3,698,349 (Stevens) discloses a seagoing barge and tug construction wherein an aft section of the barge is received between the twin hulls of a catamaran type tug. One disadvantage of this arrangement is that the forward end connection between the tug and barge does not engage enough of the barge to evenly distribute the strain. Moreover, this design includes a large number of curves and angles making the construction difficult to build. Further, because of the manner in which the barge and tug mate, substantial vertical ballasting is required to bring the two into the alignment required to bring the two into engagement.
A barge-tug construction which presents even more complex ballasting problems in providing engagement and disengagement of the tug and barge is that disclosed in U.S. Pat. No. 3,610,196 (Lowry). More specifically, the Lowry patent discloses a segmented ship system wherein a series of keys and keyways formed respectively on a portion of the tub tongue and portions of the barge that form a mating slot, are utilized to provide interlocking between the tug and barge. The locations of the keys and keyways require that the barge and tug be ballasted such that the tongue of the tug is first raised above the portions of the barge forming the slot. The tug is then moved forward and finally dropped so that the keys engage in the keyways. This engagement operation is obviously time consuming and, as noted, requires complex ballasting. Further, the interlocking shapes disclosed in the Lowry patent are extremely complex and the construction would be very difficult to manufacture.
A third patent of particular interest here is U.S. Pat. No. 3,556,742 (Gainsley) which discloses a composite barge-tug vessel made of interlockable sections wherein the tug or propulsion unit is "plugged-in" to the aft end of the barge or cargo-carrying hull. Again, the interlocking shapes employed are complex and the tug itself is of a design which is of questionable seaworthiness. In addition, engagement and disengagement require substantial ballasting to ensure proper alignment.
Other patents disclosing combination barge-tug vessels include U.S. Pat. Nos. 3,345,970 (DeLong); 3,362,372 (Peterson); 3,417,721 (Vienna); 3,492,964 (Garcia); 3,550,550 (Fletcher); 3,613,628 (Garcia); 3,735,722 (Hooper et al); 3,756,183 (Clemence, Jr.); 3,837,315 (Giblon), although it will be understood that this listing is not, nor is it represented to be exhaustive.